* In a large bowl, combine the contents of cake mix and baking soda. Add the buttermilk, eggs, food coloring and vanilla; beat on low speed for 30 seconds. Beat on medium for 2 minutes. Pour into two greased and floured 9-in. round baking pans.

* Bake at 350° for 30-35 minutes or until a toothpick inserted near the center comes out clean. Cool for 10 minutes before removing from pans to wire racks to cool completely.

* For frosting, whisk flour and milk in a small saucepan until smooth. Bring to a boil; cook and stir for 2 minutes or until thickened. Cover and cool to room temperature.

* In a small bowl, cream butter and sugar until light and fluffy. Beat in vanilla. Add milk mixture; beat for 10 minutes or until fluffy. Spread frosting between layers and over the top and sides of cake. Yield: 12 servings.